Hi Paul,
An interesting story :-) Congrats to the latest improvements!
Am 25.11.2018 20:08, schrieb N1BUG:
1. Loaded Q is much higher!!!
Expected.
2. I had to move the tap further up the coil to resonate the system
(less inductance.... or at least fewer turns).
Also expected. The suhort cut turn reduced the inductivity. Now when the
shortcut is gone, it will be higher so you need a few turns less, which
again ruduces the losses! :-)
Must be something heating up very slowly, then cooling quickly after
RF stops.
That is very strange! Thermal capacity and time constants should be the
same when heating up or down.
How much antenna current do you get at 100 W RF power?
If you say you have a scopematch, i assume you mean that you are the
curves of voltage and current on an oscilloscope, right? I have thoughts
about EMI into the power supply or exciter but this is unlikely since
you have a decoupling xfmr at the antenna feed point.
Is your antenna earth separated from the mains earth? If not, try to
separate it and see if the effect is still there, apart from the lower
antenna current.
And maybe it is worth to control the DC supply voltage of the exciter
and PA during the effect starts.
If the PA runs at 12V, use a battery and a floating signal generator.
These are my next thoughts.
73, Stefan
But I cannot find it. I think I have to buy one of the
inexpensive IR heat guns and try to examine the coil and hardware
while the TX is running. Maybe it will see something.
Now we have freezing rain and snow so I had to stop all testing. No
good wx forecast until Thursday!
73,
Paul
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